Version 6 of the popular Perl programming language will not be compatible with previous versions, but will open up a new world of custom "languages" and interpreters, according to its founder Larry Wall. Wall and his co-developers are doing with Perl 6 -- starting again. "It will break backward compatibility [but] in order to simplify it we have to get rid of old cruft, particularly the regular expression cruft," Wall said. "A lot of the unreadability of Perl is related to the regular expression syntax – and we didn't do that, we got it from Unix. It needs to be end-of-lifed."